Pressing processes of this kind are used e.g. in the pressing of pipe ends or shaft connections. A high pressing power is required because the friction of a tight fit has to be overcome and in many cases the material additionally has to be deformed. A typical example is the pressing of collet chucks or clamping sleeves into and out of corresponding tool or collet chuck holders in machine tools.
In certain embodiments of tool holding fixtures, especially those with a small or zero conicity of collet chuck and retaining cone, as are preferred for machines with very high speeds of rotation, the collet chucks or clamping sleeves with the inserted tool shank cannot easily be introduced into the retainer of the collet chuck holder and fixed with a tension nut or, conversely, withdrawn again after loosening of the tension nut, but have to be pressed in and out again using a high pressure. There are various solutions for these pressing-in and pressing-out operations, but they suffer from disadvantages.
In the clamping device described in DE-A-4405242, the forces required to close the collet chuck are applied mechanically by means of a differential threaded pinion arranged in the clamping device. The clamping device described in WO-A-98/32563 has a hydraulic system which effects an axial displacement of an outer sleeve with a flat inner cone on the corresponding outer cone of the actual tool holding fixture. Such solutions, where the devices for producing the necessary axial forces are part of the clamping device, have the disadvantage of making the clamping devices comparatively expensive. Moreover, the demand for improvement to the true running properties of clamping devices implies structural simplification, i.e. a clamping device should consist of the minimum number of individual parts and have the simplest possible geometrical design. The complexity of integrated pressing devices is in basic conflict with this principle.